Oratories



June 4, 1929.

G. w. ELMEN 1,715,541

MAGNETIC MATERIAL Filed Septv 19 1927 7 Sheets-Sheet l l 1 I 1 l l I I I l l l l 2 a 4 5 6 7 e 9 I0 mo F/a Z yan/M June 4, 1929. e. w. ELMEN 1,715,541

MAGNETIC MATERIAL Filed Sept. 19, 927 7 Sheets-Sheet 2 //v VENTOR Gusmr W [LME/V WQ/M Jun: 4, 1929. w ELMEN 1,715,541

MAGNETI C MATERIAL Filed Sept. 19, 1927 '7 Sheets-Sheet 3 F/G 6 H07 IBY aw/M June 4, 1929.

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F/QZO /Vl//VTOR Bus 741 WfL/VIE ATTORNEY June 4, 1929.

100 soc 50o G. w. ELMEN 1,715,541

MAGNET IC MATERIAL Filed Sept. 19, 1927 '7 Sheets-Sheet 6 /NVENTOR Gus TAF W [LME/V A T TORNEY June 4, 1929. G. w. ELMEN 1,715,541

MAGNET I C MATER IAL Filed Sept. 19, 1927 v Sheets-Sheet 7 i may i 3 H025 2000 1K #5 k m /NVENTOR GusrAF W [LA/[N YkJM ATTORNEY Patented June 4,.1929.

UNITED S ATES PATENT, oFricE.

GUsrAF'w. ELMEN, 0 LEONIA, nnw masniassmnon' To 'BELflirELErHoN E LAB- onaromsalnconromrnn; 02 NEW YORK, Y., Ao oR1 oRA'rron OF NEW I YORK." 1..

. MAGNETIC MATERIAL.

" j a ii'cati n sled September 19, 1e27.-seria1 mafia beer.

The present invention relates to, magnetic materials and totheir application toelectro magnetic systems, --It-has a. wide field o1i1se fulness and isof special interest in all-those cases in which the impressed magnetizing forces are small, such as in electric signaling y i :;u ':'.-'4:' Q

a Among. themore important characteristics of the materials otthis inventionarehigh permeability, especially at low magnetizing. -forces, high degree of constancy of permeability over a considerable range of magnetizing forces,-and high resistivity with consequent low edd current losses.- 1

.In-Elmens S. Patent1,5 86,884, J une- 1, 1926 tliere are'described and claimed methods of P Q i a-n Qk lmn a loys.- Qf high. pe meability.. and 40w. hysteresis loss; at mag netizing forces employed in the magnetic circuits of loaded;.co mmunieation circuits.- InU. S.;1?fatent-.-1,586,883, June {1, -1926;an'd other of. applicants patentsand applications, there are described similar compositions, and methods of producing-them, which have the additional valuable property, among others, of high resistivity imparted;to them. bythe addition of a. third element; 2'

In Elmens application serial No. 119,623, filed June 30, 1926, there are described and claimed magnetic compositions of iron, nickel, and cobalt which have been discovered to have, among other unusual properties, a very high degree of constancy of permeability over a wide range of magnetizing forces including the low range employed in loaded signaling conductors.--The utility of such compositions may be increased, especially for loading speech frequency or other high frequency circuits, by increasing their resistivity, it this be done without excessively or at all impairing other desirable properties.

Brief mention is made in that application of the addition of fourth substances such as chromium to increase the resistivity. It is in this present specification, however, that compositions including added fourth substances to increase the resistivity of compositions containing threemagnetic elements will be fully .set forth and claimed. To the extent that the subject matter claimed is disclosed in them, this application is a continuation in part of application, Serial No.- 119,623 and also application Serial'No. 119,622, filed also on Junfe 30,- 1926, Anobject of the present invention, therefore, is to. -inc rease the resistivity of magnetic materials-lmving'other desirable characteristlcsimfm i,'|;"= :E-:': '1.

Aiurtherpbject is to reduce eddy, current losses in magnetic materials of high initial permeability. 1 n r It has been found-that by the addition of molybdenum, chromium, tungsten, manganese,'vanadium, tantalum, zirconium, copper, and silicon in proper proportions, and with appropriate .heat treatments, compositions may be produced which have part or all of the desirable properties of the compositions described and claimed in application Serial No. 119,623 to, a-,greater or lesser e'x'tent,in some,.instances ;to thesa'me extent as, or greatericxtentthanwithout the added ingredient,-fand.i n. addition, a greatly increased resistivity. The production of magnetic compositions of these; characteristics which are workablefandotherwise suitable for use are of great technical importance,

Although in its -preferred'form the alloys of the present invention comprise nickel, iron, cobaltand 'molybdenum (or' chromium) properly proportioned and properly heat treated,-the nature and proportions of the constituents, especially the nature and proportions of the fourth element, as well as the nature of the heat treatment of the alloy may be modified'in order to'bring out or lay stress on any particular characteristic. 1

Manganese may be added in addition to any of the substances mentioned to increase the workability in accordance with known n'ietallurgical practice. Such instances of its use are to be distinguished from those cases in which it constitutes'the entire fourth component functioning to increase the resistivity.

It is noteworthy, that chromium, molybdenum, and tungsten, which are among those giving excellent results, are metals of the chromium group of the periodic table. Of the other elements, those which effect the more noteworthy increase of resistivity are closely related, in theperiodic table, to chromium. The expression fourth element is specifically intended to include the general case of two or more elements mixed together and functioning as a fourth element.

Three characteristic heat treatments will now be;described. -These',treatm'ents relate to pancake coils of tape material, a few thousandths of an inch thick, a fraction of an inch wide and weighing about 40 grams. The results obtainedmayvary greatly with variations of heat treatment. In particular certain desirable properties may be accentuated by particular heat treatments.

Treatment l.In-'praetice' this treatment assumed two different aspects, one being characterized by a ra'ther slo'w rateof cooling, and the'other by a relatively fast rate of cooling. The furnace used was an electric-resistance furnace capable of having-the temperature regulated accurately to any desired'value. According to the first aspect, the samples were placed into an annealingpot, heated to 1100 C., maintained at that temperature-for one hour and then cooled in the furnace at the following cooling rates: approximately 200 Cqper hour for'the'first hour, approximately 100 C. perhour for the next two hours, approximately (ES C. per hour for the next'three hours, approximately 50 C. per hour for the next four hours, and approximately 40 C. per hour until approximately room temperature was' reac'hed. We shallcall this treatment-I According to the second aspect, the samples were placed into an annealing pot and heated to 1100 'C., maintainedat that temperature for one hour, and then cooled, 100 C. during the first 23 minutes, 200 C. during the next minutes, 200 C, during the next minutes, and 100 C(during each 4-0 minutes until room temperature was reached. Ive shall call this treatment 1 T rewtment' II .This is a so-called double treatment, the first phase of the operation being substantially the same as Treatment I, namely, the samples are annealed at'1100 C., maintained at that temperatureforone hour and then cooled in the furnace as specified for treatment either I... or L; This treatment is followed by a second heat treatment consisting in placing the samples in a furnace having a temperature of about 600 (1, keeping them there for 15 minutes, then taking them out and cooling them from 600 to 400 (1., in such a fashion as to result in an average cooling rate of 1.9 C. per second. No distinction is made as to whether the first part of this treatment was in accordance with I or L, as the results would di Her only quantitatively.

Treatment [[l.This is a modification of Treatment II, characterized by a cooling rate, after reheating, of 9.5 C. per second from 600 to 400 C. instead of 1.9 C.

The properties which may be imparted to representative compositions of alloys and the methods by which this is done are described herein with reference to the accompanying drawings. Legends on these drawings and numerical values given in the text relative to magnetizing forces, coercive forces and flux densities are given in c. losses in ergs per cubic centimeter per cycle; and resistivities in microhm-centimeters.

Figs. 1 and 2 show two magnetization curves, and two permeability curves of a virgin alloy containing nickel, cobalt, iron and molybdenum, designed to graphically indicate differences in magnetic properties which may beproduced by different heat treatments;

Figs. 3 to 11, inclusive, depict the variation of permeability with varying magnetizing force-for a number of different alloys;

Figs. 12 to 22, inclusive, represent typical hysteresis loops at various values of maximum induction for typical alloys in accordance with the invention;

Fig. 23 shows graphically the variation of resistivity of an alloy of nickel and 25% cobalt, and the balance iron plus molybde num, as the molybdenum content is varied from zero to 9%.

Fig. 24 illustrates the variation in permeability for a small alternating magnetizing force upon which is superposed a steady magnetizing force, the amount of which is varied, for an alloy containing approximately Ni, 25% Co, 3.5% Mo, and the balance iron.

Fig. 25 illustrates graphically the magnetizing forces required to cause the permeability to change 1% from the initial value as a function of the molybdenum content.

Fig. 26 depicts graphs representing the initial permeability as a function of the molybdenum content according to various heat treatments;

Fig. 27 shows the percentage by which the permeability departs from the initial value at the flux density of gauss, as a function of the molybdenum content.

Fig. 28 represents the induction at which the permeability departs 1% from the initial value as a function of the. n'iolybdcnum content.

Fig. 29 shows a graph of the magnetizing forces required to cause the initial permeability to change 1% from its initial value as a function of the chromium content.

Fig. 30 shows a signaling conductor continuously loaded with a magnetic material in accordance with this invention.

The curve A of Fig. 1 represents the relation between magnetizing force H and the induced flux density B in c. g. 5. units for a virgin material containing 45.28% Ni, 21.92% Fe. 24.72% Co, 7.16% Mo, 39% M11 and .47% Si. This composition had the high resistivity of 82. It was given heat treatment I The curve indicates that at a magnetizing force of about 10 gauss the induction B is 9,500. At 50 gauss B 10,250. This compog. 8. units; hysteresis Iii) sition has been found to possess excellent properties.

Curve B of Fig. 1 shows a magnetization curve for the same composition as that of curve A, but having received a different heat treatment. Aft-er the pot annealing at 1100 C. for one hour, this material was cooled in the. furnace to room temperature, then it was reheated to about 400 C and this temperature maintained constant for a period of 55 hours; after this the samples were slowly cooled to room temperature. It is easily appreciated from the inspection of the magnetizing curve B .thatthe magnetic characteristics of the alloy were profoundly afi'ected by this different heat treatment.

However, the etfects of,.this prolonged I heating are more strikingly brought out by a comparison of the -Hp. curves illustrated in Fig. 2. Curve A of Fig. 2.1epresents the permeability variation curve of thisalloy after treatment I,,.; Curve B represents the permeability variation .after the prolonged heat treatment. As is easily seem where there is no exceptionally noteworthy constancy of permeability indicated in curve A, curve B indicates a permeability decidedly constant up to a magnetizing force of 6. lhis constancy of permeability, however, is-accompanied by considerably diminished initial and maximum permeabilitiesa- Whereasthe initialpermeability of the samples given treatment L, was 1358, it was only 575 after the prolonged treatment. This decrease in initial permeability does not only occur after such prolonged treatments, but is characteristic of any annealing operation at moderate temperatures of about ormorethan one hours duration, whenever the compositions contain cobalt, nickel, iron and molybdenum in the proportions outlined hereinafter. It also applies to those including chromium instead of molybdenunr- While this decrease in permeability cannot ordinarily be avoided by treatment-s designed to develop maximum constancy of permeability, it is compensated for by the increased constancy of permeability which is a characteristic feature of this invention. For particular purposes compositions having sufficiently constant permeability may result from less prolonged annealing at moderate temperatures. It is necessary to strike a balance between the initial permeability and the degree of constancy desired for any particular case.

The magnetizing force at which the permeability changed 1% from the initial pcrmeability was only .017 in the case of heat treatment I It was .61 after the prolonged treatment. Furthermore, the percentage change in permeability, for, B 100. was 5 85 in the first case but was only .1 in the second case. The hysteresis loops of specimens of this composition having the heat treatments specified would, for corresponding values of applied magnetizing force, possess similar striking differences-in shape and area. The difference in the magnetic properties resultingfrom different heat treatments are thus strikingly-illustrated by this example. V I Fig.3 depicts the variation of permeability with varying: magnetizing forces for-virgin materials of the following approximate compositions given heat treatment 1,:

Curve A,-50% Ni, Fe,',25% Co and 5%Mo. H

Curve B, 50% Ni, 23% Fe, 25% Co and 2%Mo.- t Curve C, Ni, 2 t%' Fe, 25% Co and 1% Mo.

Thematerial represented by curve. A had an.initial .permeabilityof 568, remaining highly constant up t( TI= 1.25 a maximum permeability of 27.50 at amagnetizing force of 2.37 gauss; ajhysteresis loss of 1060 ergs at a-flux densityof 5220,11 flux :densityof 11,150 at amagnetizing .force of 50- gauss a remanence of 4020, a coerciveifo1 'ce--of- .84: c. g. s. units; a resi stivity.of 65.5;microhm centimeters; 1% change in permeability at a magnetizing forceof 1.13; and a change in permeability for a flux density of 100.gauss of 0.16%. When this .composition was given heat Treatment II, the initial permea ility was 1628, whereas T eatment III gave an initial permeability of 1849. 1., Y

The material whose permeability variation is representedfbycurveB exhibited an initial permeabilityjof 379 which-remained constant up to a magnetizing force of almost 2.3 gauss. The maximum permeability of this composition was about 2000 corresponding to a magnetizing force of 3.45 gauss: Its hysteresis loss at an induction of 6780 was about 2010 ergs per cubic centimeter per cycle, Whereas its flux density at a magnetizingforce of 50 gauss was 12,900. It had a remanence of 7,700, a coercive force of 1.35, a resistivity of 41.55, a magnetizing force for 1% change in permeability of 2.30 and a percentage change in permeability for a flux density of 100 of 0.078.

Curve C of Fig. 3 represents a variation of permeability of a material whose initial permeability was 317. This material exhibited a maximum permeability of 1810 at H=4, a hysteresis loss of 1352 ergs per cubic centimeter per cycle at B=5725, a flux density of 13,625 gauss at H=50, a remanence of 2681, a coercive force of 1.22, a resistivity of about 31. an H for 1% change in permeability of 1.26, and a percentage change in permeability for B=100 of 0.11.

Curve A of Fig. 4 represents the variation of permeability of a virgin material containing approximately 45% Ni, 27% Fe, 25% Co, 2 Mo and 0.35% Mn, after having been given heat Treatment L. The initial permeability of this material was 534 and was constant to about H 125. The resistivability variation of a virgin alloy containing ity was 45.43.

Curve B of-Fig. 4 depicts the variation of permeability of a virgin material containing approximately 45% Ni, 29% Fe, 24 Co, 1% Mo, and 0.20% Mn given heat treatment I,,. The initial permeability of this material was 490 and the permeability was fairly constant up to about H=1.7 5. The resistivity was about 32.

Curve A of Fig. 5 represents the permeability variation of a virgin alloy containing approximately 50% Ni, 21% Fe, Co, 3.50% Mo, and 0.29% Mn, given heat treatment- I,,. This material had an initial premeability of 534, which permeability is shown to remain constant up to H=2. The resistivity was 53.7. After this material had received heat Treatment II, it exhibited an initial permeability of 1061 an d after it had received Treatment III an initial permeability of 1303.

Curve B of Fig. 5 represents the variation of permeability of a virginalloy containing approximately Ni, 16% Fe, 50% Co, 3.50% Mo, and Mn trace,.given heat treatment I The constancy of permeability extended to magnetizing forces up to about 4 gauss. The inital permeability of this alloy was 113. The resistivity was about 47.6.

Curve A of Fig. 6 represents the variation in permeability of avirgin alloy containing approximately 45%Ni, 25% Fe, 25% Co and 4.86% Cu, given heat treatment I It had an initial permeability of-27 5, a maximum permeability of 1525, at H=5; a hysteresis loss of 2010 at 13 56.50; B at H 50 of 13,900; a remanence of 2618; a coercive force of 1.494; a resistivity of 18.21; 1% change in permeability at H=3.1; and a percentage change in permeability for B I 100 of 0.02. As compared with the alloys including molybdenum the increased resistivity secured by adding copper is not noteworthy.

Virgin compositions of approximately 50% N': 20% Fe; 25% Co, and 5% Cu and 45% Ni, 20% Fe, 25% Co, and 10% Cu exhibited properties not greatly different from that of 45% Ni, 25% Fe, 25% Co and 4.86% Cu.

Curve B of Fig. 6 illustrates the permeability variation of a virgin composition containing approximately 45% Ni. 28% Fe. 25% Co and, 1.13% Cr. given treatment I,,. The initial permeability was 475. The resistivity was 32.4.

Curve A of Fig. 7 represents the variation of permeability of a virgin alloy containing approximately 51% Ni, 21% Fe, 24% Co, 3% Cr and about Mn, gix'en treatment I... This material had an initial permeability of 451 and a resistivity of 43.0. Heat Treatment II increased the initial permeability to 941 and the heat Treatment III resulted in an initial permeability of 825.

Curve B of Fig. 7 represents the permeapproximately Ni, 27 17}, Fe, 25% (lo. and 2% Cr, given treatment I The curve indicates that the permeability remained practically constant up to II abOut 1.7. This alloy had an initial permeability of a maximum permeability of 2350 at H 310; a hysteresis loss at 1120 at B 5100; B at H 50 of 13,400; a raunanence of. 23400: a coercive force of 1.08: a resistivity of 44.2"); an H for 1% change in permeability of 1.7 and a percentage change in permeability for B= of .075. Heat Treatment II produced an initial permeability of 849 and Treatment III gave an initial permeability of 1077.

A virgin alloy containing approximately 45% Ni, 27% Fe, 25% Co, Cr and 0.33% Mn, exhibited an initial permeability of about 500, a constancy of permeability up to H 110, a maximum permeability of about after heat treatment I The increase in permeability between H 1.4 and H=2.1 was striking.

Fig. 8 represents the permeability of a virgin alloy containing approximately 1505 Ni, 27% Fe, 25% (10.3% \Y 2111( 3% Mn after having been given heat treatment I The curve indicates that the permeability remained constant up to H=about 1.0. This alloy had an initial permeability of 510; a resistivity of about 34.3 an H for 1% change in permeability of 1.0; and a percentage change in permeability for B=100 of .04. After Treatment II the initial permeability was 816 and after Treatment III the initial permeability was 931.

Curve A of Fig. 0 is representative of the permeability variation of a virgin alloy containing approximately 40% Ni. 27% Fe, 24% Co, and 2.85% Tiln after treatment I,,. This composition exhibited an initial perme ability of 435, and a resistivity of about 320-, after 'lreat-ment Il the initial permeability was 860; after 'lreatment III the initial permeability was 1200.

Curve B of Fig. 9 depicts the permeability variation of a virgin material c mtaining approximately 45% Ni. 27% Fe. 25% (To. and 3% Va when given heat treatment L. This alloy had an initial permeabilitv of 340. which remained constant for l-I=ahout 1.2. The hysteresis loss was only 000 for 13 5100. The resistivity was about 42.0: H for 1) change in permeabilitv was about 1.2: and the percentage change in permeability tor B=100 was .75. Heat 'lrealmenl ll gave an initial permeability of 002 and heal Treatment III gave an initial permeability of 1143.

A virgin composition containing approximately 44% Ni, 29% Fe, 25% C0. 1% Si. and .56% Mn, exhibited an initial permeability of 347; a maximum permeability of 2120 at H 3.15; a very low hysteresis loss of 625 for B=4850; a B at H=50 of 14,000;

a remanence of 2118; a coercive force of .67; a resistivity of 28.22; an H for 1% change in permeability of 1.05; and a percentage change in permeability for ll=100 of .18 after heat treatment I Heat Treatment II resulted in an initial permeability of S52 and heat Treatment III in an initial permeability of 1085.

The curve of Fig. 10 shows the permeability variation of a virgin alloy containing approximately 44 1/2% Ni, 27% Fe, 25% Co,-2.86% tantalum and 59% Mn, when given heat treatment I This Composition had aninitial permeability of 347. The change in permeability at H=.9 was about 1%, but the increase in permeability was very little up to 11 3. The resistivity was about 30.

Fig. 11 represents the permeability vs. magnetizing force curve of an alloy containing approximately 45% Ni, 25% Co, 27% Fe and 3% zirconium. Thismaterial was given heat treatment L, It had a remanence of 2550; a coercivity of 1. 9; and a resistivity of 37. .Thepermeability varied slightly over the range H=O to H=1.25 but this variation was inconsiderable. A striking feature is the relatively small ratio of the initial to the maximum permeability.

The curves given above relate to virgin materials In practice, however, the behavior of such compositions under varying magnetizing forces is of prime importance. In general these andv other compositions of similar characteristics, when properly heat treated have the following characteristics 1. Constant or very nearly constant permeability over a considerable range of flux densities from zero upward.

2. Substantial absence of hysteresis over a considerable rangeof fiux densities from zero upward.

3. Relatively high initial permeability and high permeability at magnetizing forces within the range of flux densities utilized in magnetic materials for telephone, telegraph and (able circuits and apparatus.

4. At high flux densities the hysteresis loss. remanence, and coercive force are low.

At fiux densities above that at which the hysteresis is entirely or almost negligible, the hysteresis loop widens out and assumes a peculiar form characterized by a constriction at the origin.

(3. The resistivity is high, values up to 80 are readily secured with little or no attendant in'ipairment of other desirable properties. This is particularly true with those compositions including molybdenum.

Typical examples of hysteresis loops will now be discussed to illustrate graphically the properties (2) and (5) mentioned above.

Fig. 12 illustrates the hysteresis loops of composition of approximately 45% Ni, 26% Fe, 25% Co, 1% Mo and 2% Mn after being given heat treatment L. For magnetizing forces up to 1.57 the loop was a straight line A and no hysteresis could be detected by ordinary methods. At a maximum magnetizing force of H=2 the curve 3 resulted; the hysteresis loss was 232 ergs per cu. cm. per cycle. At H=2.14 the curve C resulted and the loss was 929 ergs.

'Figs. 13, 14 and 15 show hysteresis loops of a composition of approximately 45%Ni, 27% Fe, 25% Co, 3% Cr and 1/3% Mn after heat treatment L. The hysteresis loop of Fig. 13 was a straight line up to H=.6; at H=1.38 (Fig. 14) the hysteresis loss was 7.6 ergs per cu. cm. per cycle; at H=1.63 (Fig. 15), the loss was 132-ergs; and at H=1.9 16) the loss was 924ergs.

Figs. 17, 18 and 19 show hyteresis loops of a composition of approximately 46% Ni, 27% Fe, 24% Co, and 2.85% Mn. This is the same composition and heat treated in the same manner as that to which curve A of Fig. 9 relates.

The hysteresis loops are as follows:'

the same.

Hysteresis Maxlmqm loss in ergs magnetiz- Gun 0 ing force per per cycle The remanence and coercivity, after an applied magnetizing force of 4.3 gauss, were very small.

Fig. 23 shows the variation of the resistivity in microhms per cu. cm. of various compositions of 45% Ni, 25% Co, and (Fol-Mo) as progressively increasing amounts of iron are replaced by molybdement I num, as a function of the molybdenum content. The resistivity increases markedly with increasing molybdenum content from about at zero molybdenum up to about 88 microhms per cu. cm. when the molybdenum content reaches 9%.

Fig. 24 illustrates graphically the relation of the permeability to an alternating current magnetizing force of about .00679 gauss and suitable frequency, for example 200 cycles per second, when a steady n'iagnetizing force is superposed on the magnetic circuit, the steady force being produced by a direct current increased in small steps. The specific material to which this curve relates contained 50% nickel, 25% cobalt, 21.5% iron and 3.5% molybdenum. It was given heat treat- The arrows in this figure indicate the direction of the variation of the permeability as the direct current magnetizing force is varied. Only one half of the complete curve is shown, the gradual application and removal of magnetizing forces in the opposite sense causing the graph to substantially repeat itself at the left of the coordinate. Another characteristic of this material which is not found in ordinary magnetic materials is a higher permeability at low magnetizing forces after a direct current magnetizing force of large value has been removed from the magnetic circuit. In the case of Fig. 17 the permeability has increased from approximately 440 to 760.

Fig. 25 illustrates graphically the magnetizing forces required to cause the permeability to change 1% from its initial value as a function of the molybdenum content in a composition of 45 Ni, 25 Co and (Fe+ Mo) after heat treatment I... \Vith increasing molybdenum content the magnetizing force required to bring about 1% change in permeability has a high value up to about 41% mol 'bdenuni.

Fig. 26 represents the initial permeability as a function of the molybdenum content according to various heat treatments. The alloys considered are approximately nickel. 25% cobalt. and 30% (Fe+ lvlo). Curve III shows that heat Treatment III is conducive of the development of the highest initial permeability which reaches a peak value of about 2500 at about 4% molybdenum content. Heat Treatment- II (Curve II) develops. in general, a lower initial permeability which reaches a peak value of about 2000 at a molybdenum content of about 5.50%. Heat treatment I (curve I results in still lower initial permeabilities. the maximum occurring at a molybdenum content of about 7%. Heat treatment I (cnrveI l has a similar effect although the initial permeabilities are lower.

Tests on the same series of compositions (heat treatment I.) at magnetizing forces of c. g. s. units show that the flux density varies linearly from 15,000 gauss at 0% molybdenum to about 9,700 gauss at 8% molybdenum.

The percentage by which the permeability departs from the initial value at a flux density of B=100 is illustrated in Fig. 27 as a function of the molybdenum content for alloys containing approximately 45% nickel, 25% cobalt, and 30% (F e+Mo). Heat treatment L, is used. With increasing molybdenum content the percentage of departure in creases slightly up to a molybdenum content of about 5.50%. With heat treatment I the increase is slight up to a somewhat higher molybdenum content. I y

The induction at which the permeability departs 1% from the initial value is illustrated in Fig. 28 for various alloys of the same composition as those of Fig. 19, as a function of their molybdenum content. This reaches a maximum of about 1100 at a molybdenum content of around 4% and then very rapidly decreases to a low value at a molybdenum content of.7%.

29 shows themagnetizing forces required to cause the initial permeability to change 1% from its initial value for a composition of 45% nickel, 25% cobalt. 30% (Fe+ Cr) when given heat treatment I,,.

With the same series of compositions the flux density at which the permeability changes 1% from its initial value is high up toabout 2% chromium, and falls to lower values for greater percentages of chromium. It is about 870 at 2% chromium.

The resistivity varies from 20 at 0% chromimn to about 58 at 6% chromium.

Vith heat treatment III the initial permeability will be above 800 for all chromium contents up to 6%. Between 3% and 6% chromium values of permeability of 1600 are readily obtained. With heat Treatment II the initial permeability-is about 800 at 0% chromium and increases to about 1550 at 6% chromium. with heat treatment 1,, initial values of 1:00 occur at 0% chromium and increase to about 1200 at 6% chromium. The heat treatments giving the lower initial permeabilities result, in general, in greater constancy.

The examples herein given indicate that suitable compositions of iron, nickel, and cobalt when properly heat treated may, in addition to their other desirable properties. especially constant permeability, and low hysteresis loss. be caused to be of high resistivity. Values of resistivity of at least microhms per cu. cm. are attainable. Experiments to date indicate that the range of possible compositions with properties similar to those of the compositions mentioned but differing in degree is as extensive as the range in which iron. cobalt, and nickel alone possess unusual properties to a greater or lesser extent i. e. 9% to 81% nickel, 5% to i 80% cobalt, and -r9% to 50% iron, and that other elements or combinations of two or more elements such -as .molybdenum, chromium, etc., may be added in varying amounts up to 10% or more depending upon the particular element em'ployed..'

' All of? the compositions specifically set forth in this specification have been found to be workable by methods usually-employed;

The highest initial permeability with compositions including molybdenum andch'romium generally results .with heat- Treatment III. Greater'constancy of permeability is generally secured by heat treatment I...

A general rule is that slower cooling and prolonged maintenance at; moderate temperature'sf(400-"-.to 500 0.): gives decreased initial, but much more constant, permeability. A-heattreatment, in any particular case, will be' determined by the magnetic properties desired in a particularcomposition as :well as byeconomic-factorsJ j Certain? compositions. which are less noteworthy for their constancy of '.-permeability ha've other. exceptional "properties. This a composition of=% Ni, 20% 'Fe, 25% 'Co, 9'.1%'Mo, 05% 'Mn, '.7% Si was easily produced with :an initial permeability around 1000. The resistivity was 88. These two properties in combinationare noteworthy. Compositions including 1 around 6% "chromium may be produced-with a resistivityzof and an initiahpermeability of-over 1500.

Therela'tive values of the several compositions are dependentlupon anumber of con siderations. )Copper, although it increases the resistivity but little, or possibly none in some ,cases, may have other worth while'advantages in these particular compositions. The strain sensitiveness, tendency to stickto a loaded conductor, and other factors are material to the-value of any composition for continuous loading purposes.

'One' important-application ofthe compositions described herein is their use as loading material for continuously loaded signaling conductors such as submarine'telegraph or teleplione cables. For this purpose the magnetic material is formed by known methods into a tape of approximately .002" thickness and .020 width and applied helicallv to a conductors the method of heat treating of the magnetic material may be varied. The heat treatments described hereinafter were carried out in an electric resistance furnace.

In one instance the composite core was placed in an annealing pot which was slowly heated to about 800 C. and kept at that temperature for about one hour. After this the conductor was allowed to cool to room temperature within the furnace; this ordinarily required about 10 hours. This treatment produces fair values of initial permeability and constancy of permeability.

If, however, the greatestcon'stancy of permeability is desired, the cooling of the conductor should be interrupted ata temperature of 400:to 500. Ci this-temperature main-- tained constant for about 8 hours, and the conductor then allowed-to cool slowly to room temperature.

a If intermediate values of permeability and constancy of permeability-are desired, the lengthof time for which the conductor is maintained at a temperature of 400 to 500 C. is varied to obtain these results.

In another case the composite conductor was passed through an annealing furnace in a continuous process at such a rate as to be annealed at about 800 to 900 C. After cooling the conductor was wound in coils of large radius and again heat treated at about 350 to 450 (1, for a length of time required to bringthe initial permeability to the required value, followed by slow-cooling in the furnace.

In accordance with a modified method, after heating it to about 400 to 450 0.. it is cooled at a moderate rate, such as cooling the annealing pot and contents in air.

Ah annealing pot of large size should be employed so that the conductor may be coiled on a large radius.

Among the uses for which these materials are adapted are coil or lun'iped loading and continuous loading of carrier frequency naling conductors in submarine and land line telegraphy and telephony, loading coils for composite telephone and telegraph systems, repeating coils or transformers. especially battery supply coils. wave filter coils, certain classes of relays. high frequency electromagnetic devices and magnetic circuits of electrical measuring instruu'ients.

The several alloys herein described and others of similar characteristics mav be employed in laminated form or reduced to pow der and compressed into cores with suitable binders or insulating materials, separating the particles in accordance with methods pro posed and employed for permalloy dust cores.

What is claimed is:

1. A magnetic material including as essential elements iron, nickel, and cobalt, characterized by a high degree of constancy of permeability over a range of magnetizing forces including the range employed in con tinuous loading of electrical'signaling conductors, and including additional material to .increase the resistivity, said additional material being selected to include at least one of the following elements: molybdenum, chromium, tungsten, manganese, vanadium, tantalum, zirconium, copper and silicon.

2. A composition-in accordance with claim 1 characterized by a nickel content of 9% to 81%, cobalt 5% to. 80%, iron 9 to 50% of the niekel-cobalt-iron content and additional material up to about 10 of the entire composition.

3. A composition in accordance with claim 1 characterized in that the additional material comprises from to 10% of metal of the group of elements comprising chromium, molybdenum and tungsten.

4. Magnetic alloy having small variation in permeability over at least that range of magnetizing forces employed in continuous loading of electrical signaling conductors, containing nickel, iron, cobalt and a fourth element for increasing the resistivity thereof.

5. Magnetic alloy having negligible variation in permeability over a range of magnetizing forces including the range employed in continuous loading of electrical signaling conductors, containing nickel, iron, cobalt and a metal of the group of elements including chromium, molybdenum and-tungsten.

6. Magnetic alloy in accordance with claim 4 heat treated to have initial permeability higher than that of soft iron.

7. .Mag'netie alloy in accordance with claim 4 characterized by a resistivity of over microhms per cubic centimeter.

8. Magnetic alloy in accordance with claim 4 characterized by a permeability varying less than 1% up to magnetizing forces of .20 gauss.

9. Magnetic material having negligible variation of permeability over a substantial range of magnetizing forces comprising cobalt, nickel and iron and having its resistivity increased by the addition of molybdenum.

10. Magnetic alloy in accordance with claim 4 containing nickel, iron, cobalt and molybdenum in such proportion as to impart. a. higher resistivity than is possessed by a similar alloy with the molybdenum replaced by iron.

11. Magnetic alloy including nickel, cobalt and iron characterized by constancy of permeability over a range of magnetizing forces, having a molybdenum content of from 1% to 8% of the total.

12. A magnetic material including nickel between 9% and 81%, cobalt between 5% and 80%, iron between 9% and 50% of the nickel-cobalt-iron content, with a content of metal of the group of elements including ()lllOlTlllllTl, molybdenum and tungsten between 1% and 8%, characterized by high constancy of permeability and low hysteresis loss in wide range of magnetizing forces including the range employed in continuous loading of signaling conductors.

13. A magnetic material in accordance with claim 12, in which the nickel content is between and 60%, cobalt 10% to 50% and iron between 10% and 40% of the nickelcobalt-iron content.

'14. A magnetic material containing approximately nickel, 25% cobalt, a molybdenum content of zero to 10% and the balance iron.

15. A magnetic composition including 40% to nickel, 20% to 30% cobalt, 22% to 25% iron and 3% to 8% molybdenum.

16. The method of developing high initial permeability in a magnetic composition including iron, nickel and cobalt, comprising heating said material to a temperature between 1,000 and 1,150 C. for at least one hour. cooling said material to below 400 C. within the furnace at an average rate of 1/2 to 5 C. per minute. reheating said material to between 400 and 600 C., and cooling it at an average rate between 5 and 25 C. per second.

17. The method of developing high constancy of permeability in a. magnetic material containing nickel, cobalt and iron which comprises heating it to a temperature of about 1100 C. for at least one hour and cooling it at a rate not exceeding 200 C. per hour, and through the range 600 to 400 C. at less than 100 C. per hour.

18. The method of developing a high degree of constancy of permeability in a magnetic composition containing nickel, iron and cobalt as essential elements, which includes first heating it to a temperature above 800 C. for about one hour and subsequently maintaining it within the range of 400 to 000 C. for a plurality of hours sufficient to produce the desired constancy of permeability, and then slowly cooling the material.

19. A transmission conductor loaded with a magnetic material comprising nickel more than 9%, cobalt more than 5%, iron more than 9% and a fourth element for increasing the resistivity, characterized by a substantially constant permeability for magnetizing forces up to at least .2 gauss.

20. A magnetic material including nickel between 9% and 81%, cobalt between 5% and iron between 9% and 50% of the entire nickel-cobalt-iron content and heat treated to have desirable magnetic properties at small magnetizing forces characterized further by the inclusion of a material amount but less than 10% of material selected to include at least one of the following elements: molybdenum, chromium. tungsten, manganese,

vanadium, tantalum, ziroconium, copper and small magnetizing forces and including a silicon. substantial quantity but less than 10% of 21. A magnetic material including nickel molybdenum. 10 between 9% and 81%, cobalt between 5% In witness whereof, Ihereunto subscribe 5 and 80%, iron between 9% and 50% of the my name this 17th day of September, A. D.

entire nickel-iron-cobalt content, heat treated 1927. to have desirable magnetic properties at GUSTAF W. ELMEN. 

